1. Field of the Invention
The present invention relates generally to patch antennas for circular polarization, and more particularly to a patch antenna, in which a slot region is arranged in a radiation portion formed on a surface of a dielectric block substantially having a rectangular solid shape, thus enabling the patch antenna to substantially generate circular polarization using the radiation portion surrounding the slot region.
2. Description of the Prior Art
Recently, communication terminals using circularly polarized wave signals, such as a GPS (Global Positioning System), a DAB (Digital Audio Broadcasting), and an ETCS (Electronic Toll Collection System) have been used. As such communication systems are widely used, the miniaturization of antennas is required for them to be suitable for the communication terminals.
FIG. 1 shows a regular square patch antenna 10 as an example of such a conventional circular polarization antenna. Referring to FIG. 1, the regular square patch antenna 10 comprises a plate ground electrode 8 formed on the substantially entire regions of a first major surface 2a of a dielectric substrate 2, a radiation electrode 5 formed on a second major surface 2b to have a substantially regular square shape, and a feeding line 7 connected to the radiation electrode 5 while penetrating the substrate 2 from the first major surface 2a. The radiation electrode 5, which is a patch of a regular square, has substantially the same length as a half of an effective wavelength of a frequency. Further, the radiation electrode 5 has degeneracy separation portions 9 formed thereon by diagonally cutting two opposite corners to generate circular polarization. Accordingly, the radiation electrode 5 is separated into two orthogonal modes by the degeneracy separation portions 9. At this time, the radiation electrode 5 generates two resonance currents having a phase difference of 90 degrees therebetween and having the same intensity in the two orthogonal modes by appropriately adjusting each size xcex94s of the cut pieces of the corners, thus forming circular polarization antenna.
Such a regular square patch antenna 10 is required to be mounted on a printed circuit board (PCB) so as to be used in conjunction with various kinds of mobile communication terminals. However, as described above, a side of the radiation electrode 5, which is a regular square patch, must have a length of xcex/2, where xcex is a wavelength of a resonance frequency. Therefore, in order to miniaturize the antenna to be mounted on the PCB, the antenna must employ a ceramic body with a high dielectric constant as a substrate. However, when the antenna uses a dielectric substrate of a ceramic body, the regular square patch antenna has a problem that it has a narrow usable frequency bandwidth and is decreased in its radiation efficiency.
In order to solve the above problem due to miniaturization of the antenna, a short-type inverse F-shaped patch antenna 20 using an Electro-Magnetic Coupling (EMC) feeding method of FIG. 2a is utilized. The inverse F-shaped patch antenna 20 comprises a dielectric substrate 12 having an approximately rectangular hexahedron shape. Here, a ground electrode 13 is formed on a first major surface 12a of the substrate 12, and a radiation electrode 15 of an inverse F-shaped is formed on a second major surface 12b and extended to a side surface adjacent to the major surface 12b. A high frequency signal source transmitted to a feeding electrode 17 formed on another side surface is transmitted to the inverse F-shaped radiation electrode 15 through capacitance between the feeding electrode 17 and the radiation electrode 15. Then, the patch antenna 20 radiates some of electric fields generated between the radiation electrode 15 and the ground electrode 13 into space, such that the inverse F-shaped patch antenna 20 can operate as an antenna. In such an inverse F-shaped patch antenna 20, a length (l) of the radiation electrode 15 is xcex/4, where xcex is a wavelength of a resonance frequency, thus satisfying the miniaturization requirement of the antenna, and enabling the inverse F-shaped patch antenna to be preferably mounted on a PCB of a communication terminal.
However, the inverse F-shaped patch antenna is disadvantageous in that it has a great propagation loss due to its linear polarization characteristic, compared with antennas having circular polarization characteristic, and thereby it cannot be an effective solution for the problem.
Further, the inverse F-shaped patch antenna is further disadvantageous in that beam radiated backward is weak due to a necessary design of the mobile communication terminal, thus decreasing the transmission/reception performance of the mobile communication terminal.
In other words, as shown in FIG. 2b, the patch antenna is mounted on a backside of the terminal (in the case of a mobile phone, a position of a battery) according to the design structure of the terminal such as a normal mobile phone. In this case, the patch antenna hardly radiates beam backward by the inverse F-shaped radiation electrode. Thereby, the mobile communication terminal is decreased in its transmission/reception performance due to the weak beam radiated in a forward direction of the terminal (in the case of the mobile phone, in a direction of a speaker).
Subsequently, such antenna technical fields require an antenna having a small size to be suitably mounted on the mobile communication terminal, while having circular polarization characteristic. Moreover, in consideration of characteristic of a mounting structure of a normal mobile phone, there is required a new antenna having an intensified transmission/reception function by controlling a quantity of beam radiated backward.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a surface mounted chip antenna, which has circular polarization characteristic by forming a slot region in a radiation portion of a radiation electrode, though employing an EMC feeding method.
Another object of the present invention is to provide a surface mounted chip antenna for controlling beam radiated backward by reducing a size of a side pattern of a dielectric substrate.
In order to accomplish the above object, the present invention provides a surface mounted chip antenna, comprising a dielectric block constructed in the form of a rectangular solid having opposite first and second major surfaces; a ground electrode formed on the first major surface; a feeding electrode formed on at least one side surface of the dielectric block; and a radiation electrode comprised of a radiation portion formed on the second major surface, an open portion formed to be spaced apart from the feeding electrode, and a short portion formed for coupling the radiation portion with the ground electrode; wherein the feeding electrode is spaced apart from the open and short portions of the radiation electrode and the ground electrode by a gap region formed by exposing the dielectric block; wherein the radiation electrode includes a slot region formed by exposing the dielectric block, the slot region having one end connected to the gap region adjacent to the open portion.
In a preferred embodiment of this invention, the slot region is formed in a shape of an L, such that distribution of current generated from the radiation electrode is substantially circular in shape.
Further, in the chip antenna, the open and the short portions can be formed on the same side surface, in which the open portion is arranged in the left side of the slot region, and the short portion is arranged in the right side of the slot region.
Further, in the preferred embodiment of this invention, a quantity of beam radiated in a direction of the first major surface can be adjusted by forming a side pattern extended from the radiation electrode on a side surface opposite to the side surface on which the feeding electrode is formed.
Moreover, the chip antenna of this invention can save the dielectric material and reduce its weight by forming a through hole penetrating opposite side surfaces of the dielectric substrate.